9.6 Why does the <Backspace> key invoke help?

The <Backspace> key (on most keyboards) generates ASCII code 8.
C-h sends the same code. In Emacs by default C-h invokes
help-command. This is intended to be easy to remember since the first
letter of ‘help’ is ‘h’. The easiest solution to this problem
is to use C-h (and <Backspace>) for help and <DEL> (the
<Delete> key) for deleting the previous character.

For many people this solution may be problematic:

They normally use <Backspace> outside of Emacs for deleting the
previous character. This can be solved by making <DEL> the command
for deleting the previous character outside of Emacs. On many Unix
systems, this command will remap <DEL>:

stty erase `^?'

The user may prefer the <Backspace> key for deleting the
previous character because it is more conveniently located on their
keyboard or because they don't even have a separate <Delete> key.
In this case, the <Backspace> key should be made to behave like
<Delete>. There are several methods.

Some terminals (e.g., VT3## terminals) and terminal emulators (e.g.,
TeraTerm) allow the character generated by the <Backspace> key to be
changed from a setup menu.

You may be able to get a keyboard that is completely programmable, or a
terminal emulator that supports remapping of any key to any other key.

With Emacs 21.1 and later, you can control the effect of the
<Backspace> and <Delete> keys, on both dumb terminals and a
windowed displays, by customizing the option
normal-erase-is-backspace-mode, or by invoking M-x
normal-erase-is-backspace. See the documentation of these symbols
(see Emacs Lisp documentation) for more info.

It is possible to swap the <Backspace> and <DEL> keys inside
Emacs:

(keyboard-translate ?\C-h ?\C-?)

This is the recommended method of forcing <Backspace> to act as
<DEL>, because it works even in modes which bind <DEL> to
something other than delete-backward-char.

Similarly, you could remap <DEL> to act as C-d, which by
default deletes forward:

This method is not recommended, though: it only solves the problem for
those modes which bind <DEL> to delete-backward-char. Modes
which bind <DEL> to something else, such as view-mode, will
not work as you expect when you press the <Backspace> key. For this
reason, we recommend the keyboard-translate method, shown
above.

Other popular key bindings for help are M-? and C-x ?.

Don't try to bind <DEL> to help-command, because there are
many modes that have local bindings of <DEL> that will interfere.

When Emacs 21 or later runs on a windowed display, it binds the
<Delete> key to a command which deletes the character at point, to
make Emacs more consistent with keyboard operation on these systems.